INTERACTIONS OF BENZO(A)PYRENE DIOL-EPOXIDES WITH LINEAR AND SUPERCOILED DNA

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  • 1 January 1985
    • journal article
    • research article
    • Vol. 45  (1) , 51-56
Abstract
Previous spectroscopic studies of the major adduct formed by reaction of (.+-.)-7r,8t-dihydroxy-9t,10t,oxy-7,8,9,10-tetrahydrobenzo(a)pyrene (BPDE-I) with linear DNA were interpreted to suggest that the adduct is not intercalated in the double helix. Studies of the electrophoretic mobility of supercoiled DNA treated with BPDE-I suggest that the adduct is intercalated. The reaction of BPDE-I with supercoiled and linear DNA was studied in Escherichia coli. The kinetics of DNA-catalyzed hydrolysis and of covalent binding were similar for the 2-DNA; supercoiled DNA exhibited a 20% increase in the rate of hydrolysis of BPDE-I at low DNA concentration compared to linear DNA. Fluorescence excitation spectra and fluorescence quenching experiments provided no support for a model in which BPDE-I adducts were intercalated in supercoiled DNA. When deoxyribonucleoside adducts were analyzed by high-performance liquid chromatography, identical distributions of BPDE-I adducts were found for supercoiled and linear DNA. A previously proposed model in which the major BPDE-I adduct in both linear and supercoiled DNA exists in a conformation, allowing stacking with the neighboring base pair and introducing a kink into the path of the helical axis, was supported by the data. Although this model provides an explanation for all available experimental data, there are undoubtedly other DNA adduct conformation models which are also consistent with the data.

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